1. Field
The field of the invention is snow grooming devices for ski slopes and runs and, more particularly snow tillers for chopping and powderizing snow surfaces.
2. State of the Art
Snow grooming devices include vehicle mounted snow plow blades, compactors which firm up deep loose snow and snow tillers. The latter is a very important, perhaps principally necessary, device. It comprises an elongate device known as a cutter bar or drum, being an elongate hollow tubular member with outstanding snow chopping and pulverizing teeth. With this device, powered generally by hydraulic motors carried upon the tiller device itself, quite hard and icy paths may be efficiently converted into skiable surfaces. Typically, the cutter bar is mounted rotatably to a frame at each of its ends, inside a covering canopy sometimes called an apron and at other times called a "box". This cutter bar covering member is mounted to the same frame as the cutter bar, and terminates at a rearward edge in a snow grooming device sometimes called a smoothing bar and sometimes a snow comb. Recently, it has become popular to provide two or three such cutter bar and frames flexibly joined as units at their ends. U.S. Pat. No. 5,067,264 discloses such a cutter assembly comprising three cutter bar/frame units joined by power transmitting universal joints. Also disclosed in this patent is a tiller assembly comprising two, instead of three, such cutter bar/frame assemblies so joined and powered. U.S. Pat. Nos. 4,892,154 and 4,775,014 both disclose snow tillers having two cutter bar assemblies mounted to join together in a flexible arrangement at the center of the tiller. These disclosed arrangements require translation of the outer ends of the tiller along a bar to accommodate the flexing.
None of these tillers are adapted for independent adjustment of the cutter in elevation to work the snow at greater or lesser depths. To work the snow at greater depths requires tilting the entire tiller frame to rotate generally about the grooming end of the cutter covering structure. This is difficult, and is associated with changing the effective size of the chamber within which the cutter operates, and with greatly increased towing loads which must be overcome by the vehicle. The angle between the portion of the cover connecting with the smoothing comb or bore becomes more acute, so that drawing the comb over the tilled snow is more difficult. The internal geometry of a chamber defined by the covering apron and the surface of the snow is changed. The deeper cutting positions are accompanied by decreased chamber volumes. U.S. Pat. No. 4,775,014 in FIG. 5 discloses a capability of raising the cutter bar out of the snow and working the snow only with the snow smoothing apparatus at the rear of the tiller. However, even this is not accomplished without considerable change in geometry of the chamber beneath the covering structure.
U.S. Pat. No. 5,067,263 discloses a tiller assembly wherein the geometry of the chamber formed below the cutter covering structure may be changed by the operator in response to varying snow conditions. In this tiller embodiment, the covering structure in part comprises a flexible portion which may be altered in geometry to provide a chamber with a planar downwardly concave upper boundary. This is done with a hydraulic cylinder and ram acting upon a lever-like device, the bottom end of which is attached to the rear or trailing edge of the flexible portion. Forward movement of the connecting end of this lever buckles the flexible portion, creating the concave shape. The buckled version of the flexible sheet provides more volume within the chamber. It is maintained that the snow in the enlarged chamber continues to be pulverized the longer period of time by the spinning cutter, so as to be more thoroughly powderized. However, the bulk of the additional area is remote from the cutter, perhaps becoming substantially filled with snow. Adjustment in depth of the cutter bar into the surface of the snow in this design can also only be achieved by manipulation of the entire structure to which it is fixedly mounted, with associated difficulty in adjusting the cutting depth for varying snow conditions. Clearly, a snow tiller design for ski slope grooming is needed wherein the height of the cutter bar and the internal geometry of the cutter bar chamber may be adjusted without alteration of the attitude of the tiller upon the snow.